Sensors which convert physical quantities into electrical variables, such as changes in the current or resistance, are used in various applications, from the simple thermometer replacing the liquid-filled one to the measuring devices used for controlling complex industrial processes. The more critical the proper and reliable functioning of the sensor element, the more important it is to be able to also control its operational condition, as well as the operational condition of the associated signal processing chain, and to obtain information about the potential malfunction, so that incorrect conclusions will not be made based on inaccurate measurement results due to malfunctioning of the sensor.
Most often, the small sensor elements are integral parts of the electronics, so it is not possible to remove them for testing. Therefore the operational condition should be verifiable without having to interfere with the actual sensor element.
Known solutions for checking the operational condition comprise, firstly, the use of more than one sensor elements for the same measurement, and comparison of the measurement results obtained from these sensors. Large or altered differences between the sensor elements indicate malfunction. Another known solution is to artificially arrange in the sensor a deflection which corresponds to a specific change of the physical quantity, such that the possible changes in the operation of the sensor element can be detected by comparing the deflection generated at the time of testing to the corresponding deflection generated at the time of installing the sensor. In practice, for example in the Wheatstone bridge connection, the testing deflection can be provided manually with a coupler that couples an additional resistance in parallel with one of the resistors.
Problems of the known solutions include complexity and consequently high expenses, manual operation and interference produced in the measurement signal by the additional components that are connected to the measuring circuit for testing. The objective of the invention is to alleviate these problems.